Proprioceptive uncertainty promotes the rubber hand illusion

Vision, touch, and proprioception contribute to body ownership, i.e., the multisensory perception of limbs and body parts as one’s own. Recently, the emergence of body ownership illusions such as the visuo-tactile rubber hand illusion has been quantitatively described by Bayesian causal inference models in which the observer computes the probability that visual and tactile signals come from a common source. Given the importance of proprioception for the perception of one’s own body, we hypothesized that proprioceptive information and its relative reliability also impact this inferential process. We used a detection-like task based on the rubber hand illusion paradigm where participants were asked to report whether the rubber hand felt like their own (illusion) or not. We systematically manipulated the degree of asynchrony of visual and tactile stimuli delivered to the rubber hand and the hidden real hand under two different levels of proprioceptive noise achieved by delivering low-frequency muscle vibration (20 Hz) to the lower arm’s antagonist extensor and flexor muscles (biceps and triceps). As hypothesized, we found that the probability of the emergence of the rubber hand illusion increased with proprioceptive noise. Moreover, fitting the data to a Bayesian causal inference model of body ownership revealed that the influence of proprioceptive uncertainty on the emergence of the illusion was captured by a change in the a priori probability of a common cause for vision and touch. Collectively, these results offer new insights into how proprioceptive uncertainty determines the rubber hand illusion and the multisensory perception of one’s own body.